This invention relates generally to devices for the movement of transducer heads to and from an operative position with respect to a stack of rotating magnetic disks in a disk storage system, and, more particularly, to improvements in these devices to minimize disk wear and to retract the heads in the event of a power failure.
Magnetic disk storage systems are widely used to provide large volumes of relatively low cost, computer accessible memory or storage. A typical disk storage device has a number of disks coated with a suitable magnetic material mounted for rotation on a common spindle, and a set of transducer heads carried in pairs on elongated supports for insertion between adjacent disks, the heads of each pair facing in opposite directions to engage opposite faces of the adjacent disks. In normal operation, a linear actuator, in response to control signals from computer, positions the transducer heads radially for recording data signals on or retrieving data signals from a preselected one of a set of concentric recording tracks on the disks.
The transducer heads, one moved to their operative position adjacent the disk surfaces, are usually restrained from actual contact with the surfaces by a cushion of air formed by the rapid rotation of the disks, but when the heads are initially "loaded", or moved to the operative position on the disks, some contact may occur until the air cushion builds up, and the disks may thereby suffer slight but cumulative surface damage due to abrasion at the areas of contact. A related problem is the sometimes irreparable damage that can result from an electrical power failure which slows the disks and allows the heads to settle into contact with the disk surfaces.
In previously available disk storage devices of the general type described, disk wear on loading the heads is confined to surface areas outside the outermost recording track by always loading the heads near the peripheries of the disks. Typically, the heads in these devices are urged toward the disk surfaces by springs or by torsion bar action of the head supports. A number of fixed camming surfaces are positioned adjacent the disks to load or unload the heads, i.e. to move them toward or away from the disk surfaces at positions near the disk peripheries, as the heads are inserted between or withdrawn from the disks. Thus, there is significant and cumulative wear near the disk circumferences, and, although the recording tracks themselves are unaffected, a significant area of each disk is unavailable for recording purposes, and the continuing abrasive wear can lead to fouling of the heads and other parts.
A possible solution to this problem is to mount the camming surfaces for movement with the heads, and to provide for relative movement of the camming surfaces and heads only during loading and unloading operations. However, this greatly increases the mass that must be moved by the linear actuator, and precludes high speed operation of the disk storage system.
The related problem of possible damage to the disks in the event of a power failure has, in previously available disk storage systems, required the use of capacitors, or an alternate power source, to supply enough electrical energy to the actuator to retract and unload the transducer heads from the disks after the power failure has occurred. This approach is not completely reliable, however, depending as it does on electrical components which may never be adequately tested until they are actually called into use. Also, a broken wire to the actuator coil would deactivate the actuator.
It will be apparent, therefore, that there exists a considerable need for a reliable means of loading the transducer heads in magnetic disk storage systems without incurring any substantial disk wear, and of unloading and retracting the heads without disk damage when the power fails or is turned off. The present invention fulfills this need.